Helmet testing equipment and methodology

ABSTRACT

A method for testing a helmet for effectiveness of user protection includes moving a load along a predetermined path, supporting a target body at an impact location in the predetermined path, the target body including a head model and a helmet disposed on the head model, and impacting the target body with a force generated by the moving of the load. The impacting of the target body entails contacting the target body with an impactor free to move perpendicularly and tangentially relative to a surface of the target body. The supporting of the target body is at least reduced, if not eliminated, before or during the impact of the impactor with the target body at the location. Forces generated are automatically measured or sensed during the impact of the impactor with the target body at the location.

BACKGROUND OF THE INVENTION

This invention relates to a method for testing personal safetyaccessories such as helmets. This invention also relates to associatedapparatus for carrying out testing protocols.

It has been widely reported during the past 20 years that the collisionsexperienced by participants in contact sports and other potentiallyinjurious endeavors are often strong enough to give rise to mildtraumatic brain injuries (MTBI) such as concussions. It is a commonoccurrence in American football for impact speeds to exceed 20 mph (9m/s), creating linear head accelerations exceeding 100 g's andconcussion risks exceeding 70%. This has created a health hazard ofepidemic proportions, with several million incidents of MTBI occurringyearly at all levels of play in all sports. (American football has thehighest incidence, and it is estimated that nearly one-third of allretired NFL players will develop some level of long-term neurologicaldisease.) In response to the MTBI epidemic, more protective helmets havebeen introduced and used by participants in sports and other endeavorssuch as car and bicycle racing, but the frequency of MTBI has remainedalarmingly high. It was recently reported that a study of the brains of111 (deceased) former NFL players revealed that 110 of them had ChronicTraumatic Encephalopathy, the degenerative MTBI caused by repeated blowsto the head.

The first line of defense against MTBI for contact game participants istheir protective helmet. It is therefore of the utmost importance thatthese helmets provide as much protection for the user as possible. Thishas been recognized since the early days of American football, but itwas not until 1973 that a serious effort to measure the protectivecapability of helmets was made by the National Operating Committee onStandards for Athletic Equipment (NOCSAE). NOCSAE introduced a helmettesting method and related standard (described below) that provided ameans to compare the protective performances of various helmets. Thisprotocol, which has been updated numerous times, was a first attempt toinsure that the helmets used in football games were compliant with astated performance standard. This standard has been adopted by manysports associations and, along with sensible rule changes regardingtackling, has played an important role in the attempts to reduce MTBI.Subsequent to the introduction of the NOCSAE standard, there have been anumber of other proposed helmet testing devices and protocols. It willbe demonstrated below that all of these protocols are inadequate becausethe impacts they analyze, generated using testing laboratory (lab)equipment, differ in significant ways from the impacts experienced bygame participants. Also; the existing standards only relate to headaccelerations resulting from impacts, but ignore the equally importantdistribution of impact-created forces transmitted through helmets onto auser's head. It is believed that these limitations contribute to thecontinued frequent occurrence of MTBI in contact sports. (Anothercontributor is the inadequate protective capabilities of availablehelmets.)

Prior Art

a. Current NOCSAE Standard Drop Test Method

In this method, illustrated in FIG. 1, a helmet to be tested is affixedto a Hybred III (H3, described in humaneticsatd.com/crash-test-dummies)head-form 1101 attached to a rigid aluminum frame 1102. The frame 1102is constrained to slide, from a specified height, down a pair ofvertical wires 1103, so that the head-helmet 1101 falls onto a fixedmetal anvil 1104 covered with a firm rubber pad (not separatelydepicted). The head-helmet 1101 is oriented on the frame 1102 such thatthe impact with the anvil 1104 occurs at a prescribed location on thehelmet. There are three possible headform weights (9.1 lb, 10.8 lb, 13.1lb). Accelerometers attached to the head-form record the acceleration ofthe head-helmet 1101 during the impact with the anvil target 1104. TheNOCSAE standard states that the severity index (SI) evaluated from therecorded acceleration profile is less than a specified upper bound whenthe head-helmet impacts at a specified speed. (The SI is required to beat most 300 s for a 11.34 fps impact speed (drop height of approximately2′), and at most 1200 s for a 17.94 fps speed (drop height ofapproximately 5′)). (An updated complete description of the NOCSAE testmethod and standard is contained in NOCSAE DOC ND 001-13m14c.)

b. Proposed NOCSAE Standard Linear Impact (LI) Test Method

In this method, the helmet to be tested is affixed to a H3 head-formattached to a H3 neck and torso mounted on a translating joint attachedto an adjustable table. The impactor is a hemispherical solid coveredwith foam padding and a urethane helmet shell. It is attached to ahorizontal cylindrical piston, guided within a straight cylindrical tubeby linear bearings, and propelled by a compressed air cannon. (Theimpactor with attached piston travels 10 cm after striking the helmetand is then stopped by a breaking cylinder and allowed to reboundbackwards within the guide. The H3 dummy is instrumented withaccelerometers, load cells, and potentiometers to record responses. Asfor the drop test standard, the linear impactor standard states that theSI evaluated from the recorded acceleration profile is less than aspecified upper bound when the impactor strikes the target helmet at aspecified speed. (A complete description of the NOCSAE LI test method iscontained in NOCSAE DOC ND 081-04m04.)

c. Pendulum Impact Test Method

In this method, a helmeted H3 head with neck is impacted by a domedspherical surface attached to a weighted pendulum that rotates downwardabout a fixed horizontal axis. The head is instrumented to measuretranslational and rotational acceleration, and the head orientation isadjustable to enable impacts at various locations on the helmet.(Methods a-c, and related methods, are described in detail and evaluatedin Pellman et al, Neurosurgery 58:78-96, 2006.)

d. Deficiencies in Prior Art Methods

The above test methods, and all others known to us that have beenimplemented or proposed, create impacts that are very different fromthose (essentially unconstrained free body) impacts that arise in thefield. The most important of these differences are described below.

In the current NOCSAE method (a), the impacting head-helmet isconstrained to descend down and rebound back up in a purely verticaldirection. Field impact rebounds on the contrary almost always occur atangles that differ significantly from the incident angle. (See FIG. 2)Also, in the current NOCSAE method, the target is fixed and thereforeeffectively infinitely heavy and completely constrained. There are otherdeficiencies with this method. One issue is the limited impact speedsthat are available. (A 20 mph impact would require a drop height of over13.5′.) Another issue is the limited number of head weights that areused. The SI evaluated from impacting a 13.1 lb head could have acompliant value whereas the SI that arises from impacting a lighter headat the same speed could be non-compliant. In that case, a complianthelmet could place the player with the lighter head at risk. Anotherissue is the fact that the method can only measure translational but notrotational acceleration. Also, measuring only the applied accelerations(and corresponding forces) ignores the (previously unrecognized) factthat the transmitted forces applied to the head can be larger than thoseapplied to the helmet at times during the impact, and ignores the degreeto which these forces can be spread out by a helmet.

A more recent use of NOCSAE-style drop impacts is the STAR helmet ratingsystem. The STAR rating of a helmet is the theoretical number ofconcussions a player using the helmet would sustain in one season. It isbased on an assumed injury risk function for each measured peakacceleration and an assumed head impact exposure matrix, estimated byusing published measurement data and on a number of simplifyingassumptions. STAR is an innovative first attempt to quantify helmetperformance in terms of a single number, it has all of the same defectsas the ones stated above, and others related to the various assumptionsand approximations involved.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide improved helmettesting devices and/or apparatus that generate impacts that replicatefield impacts more realistically than conventional testing devices.

It is a further object of the present invention to provide improvedmethods for testing the safety of protective gear such as helmets.

Another object of the present invention is to provide such testingdevices, apparatus and/or methods that facilitates the collection oftest data pertaining to important characteristics of test impacts.

The present invention contemplates the provision of data analysisprotocols that facilitate an accurately evaluation and comparison of theprotective capabilities of helmets and that effectively summarizecharacteristics of helmet safety.

These and other objects of the present invention will be apparent fromthe drawings and descriptions herein. It is to be noted that any singleembodiment of the invention may not achieve all of the objects of theinvention, but that every object is attained by at least one embodiment.

SUMMARY OF THE INVENTION

The present invention provides devices and protocols that accuratelyevaluate and compare the protective capabilities of helmets, and thatthe present impact measurement devices may be used to closely replicatefield impacts. The present devices and protocols are effectivelyutilized in an attempt to reduce the frequency of minor traumatic braininjury (MTBI).

The proposed NOCSAE LI method (b) described above is an improvement inthat both the impactor and the target have finite weight, and largeimpact speeds are readily obtainable. However, the impactor is even morehighly constrained. Before, during, and after the impact, the impactingelement and attached piston are constrained to move in a purelyhorizontal direction, whereas field impact rebounds almost always occurat angles that differ significantly from the incident angle (FIG. 2).Furthermore, the impactor does not interact with the target in a naturalway as a free body, but instead it is artificially forced to stop itsforward motion after it travels 10 cm after striking the helmet. Also,the H3-helmet target is artificially constrained by it's attachment to atranslating joint. This constraint, the horizontal direction impactingconstraint, and the external impact termination render the impacts to bevery different from field impacts. Also, as with the NOCSAE drop method,only a limited number of head weights are used, and transmitted forcesand their distributions are not measured. (Consequences of these defectscould help explain why the LI method, introduced in 2006, has yet to beincorporated into a NOCSAE standard.)

The pendulum method (c) described above, and all other reported methods,has similar issues: constrained impacts and rebounds, limited impactspeeds, and limited number of head weights. Furthermore, none of thesemethods involve measurements of transmitted force distributions.

A method for testing a helmet for effectiveness of user protectioncomprises, in accordance with the present invention, (1) moving a loadalong a predetermined path, (2) supporting a target body at an impactlocation in the predetermined path, the target body including a headmodel and a helmet disposed on the head model, (3) impacting the targetbody with a force generated by the moving of the load, the impacting ofthe target body including contacting the target body with an impactorfree to move tangentially relative to a surface of the target body, (4)at least partially reducing the supporting of the target body before orduring the impact of the impactor with the target body at the location,and (5) automatically measuring forces generated during the impact ofthe impactor with the target body at the location.

The load may include or consist of the impactor. In that case, themoving of the load includes restraining the impactor during an initialportion of the predetermined path and further includes at leastpartially eliminating the restraining of the impactor at or prior toimpact of the impactor with the target body at the impact location.

The moving of the impactor may comprise operating a cannon device topropel the impactor toward the impact location.

Where the impactor is a contact element resting on the helmet of thetarget body, the moving of the load may comprise sliding the load, orweight, down a fixed vertical rod onto a spring inserted into thecontact element.

In one set of embodiments of the present invention, the impactor isconnected to a rotatably supported rod. In that case, the moving of theload comprises rotating the rotatably supported rod at an acceleratingangular speed. The method further comprises inserting the target bodyinto the predetermined path at the impact location after and only aftera desired impactor speed is attained.

The supporting of the target body at the impact location may includesuspending the target body by elongate tensile members attached to anelement configured to release the elongate tensile members. The methodthan further comprises operating the element to release the target bodyprior to the impact of the impactor with the target body or in responseto engagement of the impactor with the target body.

In an alternative embodiment of the present invention, the supporting ofthe target body at the impact location includes supporting the headmodel on a rod attached to a holder or bracket via a plurality ofsprings each extending at least partially transversely orperpendicularly to the rod.

The automatic measuring of forces preferably includes operating aplurality of force sensors spaced from one another on the head model.The force sensors are preferably disposed between an inner surface ofthe helmet and an outer surface of the head model.

The method may additionally comprise operating a computer or processorto determine impact acceleration data including maximum recordedacceleration, average recorded acceleration, total impact time, severityindex, and coefficient of restitution.

A target body for safety testing comprises, in accordance with thepresent invention, a head model, a helmet mounted to the head model, aplurality of force sensor units distributed over the head model, and amounting plate or base platform attached to the head model, the forcesensors being adjustably attached to the mounting plate or baseplatform.

Each of the force sensor units may comprise a tube, a post, acompression spring, and a load cell. The post is slidably insertedwithin the tube and rests on the compression spring, while thecompression spring is in turn in operative (possibly indirect) contactwith the load cell. The post has an upper section extending out of thetube and terminating in an enlarged head with a convex curved surfacedisposed in contact with the inner surface of the helmet. The tube maybe a main tube having a threaded bottom section that screws into athreaded concentric lower tube that is attached to the mounting plate orbase platform. In that event, the height of the main tube is adjustableby rotating the main tube within the threaded concentric lower tube. Thelocation of the main tube on the mounting plate or base platform may beadjustable by sliding the threaded concentric lower tube in a slit orslot in the mounting plate or base platform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic elevational view of a prior art device fortesting helmet safety.

FIG. 2 is a diagram of motion of one substantially free object such as ahelmeted head impacting against another substantially free object suchas a shoulder pad.

FIG. 3 is a plot of acceleration V. time during an impact of objectssuch as diagrammed in FIG. 2.

FIG. 4 is a schematic side elevational view, partially in longitudinalcross-section of a cannon device in accordance with the presentinvention, for implementing an associated testing method also inaccordance with the invention.

FIG. 5 is a schematic side elevational view of a compression/releasemechanism included in the cannon device of FIG. 4.

FIG. 6 is a front elevational view of a ratcheting flange nut optionallyincluded in the compression/release mechanism of FIG. 5.

FIG. 7A is a schematic front elevational view of a holding and releaseassembly alternatively utilizable in the cannon device of FIG. 4 tolock, compress, and release a compression spring thereof.

FIG. 7B is a schematic front elevational view of a cylinder included inthe assembly of FIG. 7A.

FIG. 7C is a side elevational view of a gear included in the assembly ofFIG. 7A.

FIG. 8 is a schematic side elevational view of a helmet testingapparatus in accordance with the present invention, dropping a helmetonto an anvil.

FIG. 9 is a schematic side elevational view of a helmet testingapparatus in accordance with the present invention, dropping animpacting element onto a helmet.

FIG. 10 is a schematic perspective view of a sensor assembly inaccordance with the present invention, incorporable into a target bodyincluding a helmet attached to a head model.

FIG. 11 is an exploded side elevational view, partly in longitudinalcross-section of a sensor unit included in the sensor assembly of FIG.10.

FIG. 12 is a schematic side elevational view of another helmet safetytesting apparatus in accordance with the present invention.

FIG. 13 is a schematic side elevational view of an elaboration of thehelmet testing apparatus of FIG. 12.

FIGS. 14A, 14B and 14C are diagrams, partially in block form, showingsuccessive stages in the operation of a rotational helmet safety testingapparatus in accordance with the present invention.

FIGS. 15A and 15B are schematic partial side elevational views of amodification of a rotating arm and attached impactor included in therotational helmet safety testing apparatus of FIGS. 14A, 14B, and 14C,showing successive stages in the use of operation of the modification.

FIGS. 16A, 16B and 16C are diagrams, showing successive stages in theoperation of an alternatively modified rotational helmet safety testingapparatus in accordance with the present invention.

FIGS. 17A, 17B and 17C are diagrams, showing successive stages in theoperation of another alternatively modified rotational helmet safetytesting apparatus in accordance with the present invention.

FIG. 18 is a schematic side elevational view of a target body holder ormounting device with springs for stabilization, pursuant to the presentinvention.

FIG. 19 is a schematic top view of the target body holder or mountingdevice of FIG. 18.

FIG. 20 is a schematic side elevational view of a target body suspensiondevice in accordance with the present invention.

FIG. 21A is a schematic longitudinal cross-sectional view of aforce-responsive releasable coupling utilizable in the target bodysuspension device of FIG. 20.

FIG. 21B is a schematic transverse cross-sectional view taken along lineXXI-XXI in FIG. 21A.

FIG. 22 is a plot or graph of impact acceleration, in gravity units, asa function of time, in units of seconds*10⁵, obtained via testingapparatus pursuant to the present invention.

FIG. 23 is a graph of harmonic fit (light curve) to the accelerationprofile of FIG. 22 (dark curve).

FIG. 24 is a graph of five harmonics used in the fit of FIG. 23 to theacceleration profile of FIG. 22.

FIG. 25 is a graph of force applied to a test helmet or target body byapparatus in accordance with the present invention, as a function oftime.

FIG. 26A is a set of five graphs of force transmitted through a testhelmet to a head model in response to the applied fore of FIG. 25, asmeasured by five sensor units as shown in FIGS. 10 and 11.

FIG. 26B shows a graph (light curve) of a sum of the five force graphsof FIG. 26A, together with the applied force graph of FIG. 25.

FIG. 27 is a graph showing applied force as a function of time asmeasured for a helmet test object using the apparatus of FIG. 8.

FIG. 28 is a graph showing applied force as a function of time asmeasured for a helmet test object using the apparatus of FIG. 4.

FIGS. 29A and 29B are respectively photographs of a prototype of thecannon device of FIG. 4 and a suspended target body as in FIG. 20,showing a test impact before and after the impact.

DETAILED DESCRIPTION

The collisions between participants in contact sports are substantiallyunconstrained free body impacts. Although the colliding players areoften in contact with the ground at least part of the time during thecollision, these players act as essentially free bodies because thecontact forces experienced during collisions are much greater than theother forces (gravity and ground reaction forces) acting on them. (Theacceleration of gravity is 1 g and the ground reaction acceleration(force/weight) is less than 3 g, whereas impact accelerations oftenexceed 100 g.) Furthermore, for the collisions involving the heads ofthe participants, the interaction with the ground is irrelevant becausethe impact lasts only about 2 ms and is therefore over by the time theresponse to the impact travels from the player's head to the ground andback. (An exception is when the collisions occur between a head and theground.)

Although the colliding players are essentially free bodies, their headsthemselves are of course not completely free because they are attachedto necks, and the necks are attached to torsos. The strength andphysical state of these attachments during an impact determine theextent to which they are relevant to the effect of the impact on thebrain. These attachments can be modeled in a lab device by affixingelastic elements to a head model and choosing an appropriate weight ofthe resultant head-neck-torso model. The strength and placement of theelastic elements, and the weight of the model, should span the range ofpossible values as determined by biomechanical studies. Since it isessential that none of the game participants are subject to anunnecessary risk, the present invention prescribes that the lab modelhead (or head model) should have a minimal weight since this choice willgive rise to the maximum head acceleration arising from a given impactlocation and speed. If the impact metrics measured using this lowestweight value are below the level believed to create MTBI, then thesemetrics will be below this level for all of the game participants.

The present invention recognizes the importance of reducing constraintson impacted and impacting objects in order to more closely simulateactual field conditions. It was stated above how the prior-art testingmethods create impacts that differ significantly from field impacts. Itis to be demonstrated how the artificial constraints placed on impactsby prior art methods can drastically change the nature of the impacts.In an unconstrained impact of one object onto another at an obliqueangle, the velocity of the impacting object will decrease in thetangential direction because of the sliding friction between theobjects, and the velocity will decrease in the perpendicular directionbecause of the elastic damping between the objects. The rebound anglewill therefore be very different from the incident angle, and therebounding object will acquire rotational, as well as linear, motion.

A diagram of this process is illustrated in FIG. 2. An incoming curvedobject 1105 such as a helmet strikes a second object 1106 such asanother helmet or a shoulder pad at an oblique angle along a path 1107.During the brief period that the objects 1105 and 1106 are in contact,the first object 1105 slides over the second object 1106 as theycompress together. This tangential sliding motion 1108 is opposed by thesliding friction force, which exerts a torque on the first object 1105,causing it to rotate forward, as indicated at 1109. When the objects1105 and 1106 separate after they compress and decompress, the firstobject 1105 rebounds at a generally different oblique angle along a path1110, with a velocity and spin determined by the incident velocity, themasses and curvatures of the objects 1105 and 1106, the coefficient ofrestitution between the objects, and the coefficient of sliding frictionbetween the objects. This natural interaction, which proceeds accordingto the laws of free-body mechanics, is very different from the unnaturalimpacts produced by the prior art testing devices. In terms of thisexample, these devices artificially constrain the incoming object torebound in exactly the same direction as the initial direction, with noacquired rotation. A consequence of this is that the force andacceleration profiles associated with the impacts created byconstraining testing equipment do not correctly replicate the profilescreated in game impacts. The artificial constraining forces act onimpacted helmets and distort the shape and magnitude of the measuredforce profile from the profile that would result from a natural impact.

As explained above, one of the consequences of using constrained impactsto test helmet performance is that the forces and torques exerted on ahelmet arising from such impacts are different from those arising fromunconstrained impacts at the same location and velocity. Theperpendicular components of these forces are often similar, but the(torque causing) tangential components are usually very different. Thetangential component of a constrained force depends on the impact speedand the masses and elasticities of the colliding bodies, whereas thetangential component of an unconstrained force depends in addition onthe more detailed properties of the bodies such as their curvatures,moments of inertia, and sliding friction coefficients. Depending on thevalues of these quantities, the applied tangential constrained force canbe considerably more than or less than the tangential unconstrainedforce. The use of constrained impacts therefore introduces large anduncontrolled elements of uncertainty into the force and torquemeasurements. Such impacts can therefore not be expected to provide anaccurate description of realistic game impacts.

Another way of stating the problems associated with using constrainedimpacts is that such impacts impart unphysical forces and torques onto astruck body (forces that are not created in game collisions), inaddition to the physical forces and torques imparted in an unconstrainedimpact. These artificial forces are those required to maintain theconstrained motion of the impacting body and to compel the impactor torebound in the same direction as the incident direction. The total forceexerted on a body in a constrained impact is the vector sum of thephysical force and the constraining force. It can be significantlydifferent from the physical force in both magnitude and direction.

Discussed hereinafter are force profiles arising from both constrainedand unconstrained impacts onto a helmet from the same impactor at thesame location and speed. These profiles are seen to differ from oneanother in important ways, demonstrating how constrained impacts lead tounreliable impact data. Slow motion videos also demonstrate the physicalconsequences of free body impacts described above. These show thatrebound direction differs significantly from incident direction and thata bounding impactor acquires a rotational motion.

The method and associated devices of the present invention take intoaccount the above described physical effects during impacts, such assliding and rotating, and provides for measuring transmitted forces,which is not included in prior art approaches.

The present invention provides laboratory football helmet testingapparatus and methodology that closely replicates or simulates impactsbetween football players that occur in football games and practices. Theinvention further contemplates a comparison of the impact data measuredin the lab test with those measured in the field, under the same initialconditions. The lab conditions (impact locations and velocities,impactor and target weights, constraints, etc.) are all controllable andmeasurable, but the field conditions must be taken as they occur. Thedata on field impacts is correspondingly much less accurate anddetailed.

One category of field data consists of measurements recorded onaccelerometers placed at various locations on the inside of helmets.These data specify the magnitudes and approximate locations of theimpacts, but do not specify the impact velocities, the helmets used, orthe relevant body-part weights of the players. Another category of fielddata consists of impact speed measurements taken from video recordingsof game impacts that resulted in concussions. These speed measurementswere, however, not accompanied by measurements of the corresponding headaccelerations. These head accelerations were therefore estimated byusing lab measurements of the head accelerations arising from themeasured impact speeds.

None of these investigations have correlated the speed or accelerationmeasurements with the weights of the players involved. Also, it isnecessary to supplement the speed measurements with lab accelerationmeasurements in order to estimate the associated accelerations, and tosupplement the acceleration measurements with lab speed measurements inorder to estimate the associated speeds. Furthermore, without theassociated weight information, it is not possible to accuratelydetermine the speed or acceleration levels that are likely to causeMTBI. For example, an impact on a player at a measured speed that didnot result in a concussion could have resulted in a concussion in aplayer with a smaller head weight.

The testing of helmets in a lab setting serves two important functions:(1) It provides information that gives a more complete description offield impacts by supplementing the directly measured field impact datawith lab impact data, and (2) it provides a framework for the testingand certification of helmets in order to insure that compliant helmetsprovide as much user protection as possible. For each of thesefunctions, it is crucial that the lab testing impacts replicate thefree-body field impacts as closely as possible. A preferred way ofaccomplishing this pursuant to the present invention is to have a labimpactor moving as a free body during the entire impact time, and tohave the target (e.g., helmet and head model, with or without torso,attached to one another) free to react in the way that a free bodyreacts. In addition, the present invention contemplates that impactorand target weights and elastic constants to cover the entire range ofencountered field values. In particular, preferred impacting weights arerelatively large, and preferred target weights are relatively small, inorder to maximize the target acceleration that occurs at a given impactspeed. If these colliding elements create a head acceleration profilethat is considered safe, then the elements of all occurring weights willdo the same, whereas the converse is not true.

Lab measurements are of course much more informative than fieldmeasurements. For each impact, using a specified impactor and target,the impact velocity and location, the helmet used, and the head weightsare known, and the resultant head accelerations (and preferably otherquantities such as transmitted forces) can be accurately measured andused to evaluate performance metrics such as peak accelerations andseverity indices.

To compare lab and field measured accelerations in a model-independentway, metric values derived from the respective acceleration and forcedata can be directly compared. Some relevant metrics include the peakand average recorded accelerations, the SI, the impact duration, and theFourier series expansion coefficients of the acceleration data. Asexplained above, the prior-art testing devices create impacts thatdiffer significantly from field impacts. These differences are notalways apparent from comparisons of the acceleration profiles of the laband field impacts corresponding to the same impact speed. Plots of bothprofiles have the same general form exhibited in FIG. 3, in which theabsolute value of the acceleration (measured in units of theacceleration of gravity g) is plotted against the time evolved duringthe impact. The typical plot in both cases curves upward from the startof the impact, reaches a maximum, and then curves back downward,initially more rapidly and then more gradually. The differences betweenthe profiles are in the details, and the validity of a testing method isdetermined by how well it minimizes these differences.

These issues are not academic. Since measured field acceleration dataare usually not accompanied by the corresponding impact velocity values,lab data are used to estimate these velocity values from the measuredfield acceleration data. If the lab data are obtained from unrealistichighly constrained impacts, the derived relation between labacceleration values and lab impact velocity values cannot be reliablyused to estimate field impact velocity values from field accelerationvalues.

The impacts that arise in preferred embodiments of testing equipmentpursuant to the present invention are much more realistic. Impactor andtarget as disclosed herein are preferable completely or substantiallyfree and unconstrained before, during, and after an impact.

Of course, any lab device that attempts to replicate actual collisionsbetween game participants will necessarily do so in an approximate way.The advantages of well-executed lab measurements are that they arecontrolled, accurate, and repeatable, but since they necessarily involvesimplifications and compromises, they cannot be expected to predictperfectly the outcomes of the highly complex collisions between livingsystems. The lab equipment comprises a given fixed mechanical system,with a limited number of possible configurations and adjustments,whereas all humans differ from one another in infinitely many ways,including differences in their body structures, their mental andphysical response mechanisms, and their instantaneous state of motionand muscle tension.

Given inherent limitations of lab devices, it is important that helmettesting methods at least provide impacts that reproduce unconstrainedfree body collisions as closely as possible. Because the existingmethods fail to provide such impacts, there is a definite need for morerealistic testing methods. In the following, preferred embodiments ofsuch methods are described.

FIG. 4 depicts a cannon device that propels a helmet-shaped impactingelement 2 (impactor) at a target body (see, e.g., FIG. 20) consisting ofa helmet attached to an instrumented head-neck-torso model. Although thecannon propulsion mechanism can be based on compressed gas, hydraulics,or other similar materials, preferred embodiments are spring-loadeddevices. In these cannons, the impactor is in contact with a spring thatis compressed and then released in order to propel said impactor towardsthe target. The target body is preferably initially supported from aboveby attached thin wires or similar elements. (FIG. 20, below.) The targetbody is released prior to the impact or after a small force is appliedto it, so that both the impactor and target are completely free duringthe impact.

The cannon device of FIG. 4 comprises a cannon body 1 consists of threeconcentric cylindrical horizontal chambers 1′, 1″, 1′″ connected inseries. A forward (target-facing) largest diameter (front) chamber 1′holds an impactor 2, a smaller diameter central chamber 1″ holds aconcentric helical compression spring 3, and a backward-facing evensmaller diameter (rear) chamber 1′″ accommodates a concentric flange nutwinding cylinder 4. The front chamber 1′ has a diameter slightly greaterthan that of the impactor 2, and the central chamber 1″ has a diameterslightly greater than that of the spring 3. A compression/propulsionelement 5 includes three cylindrical sections connected in series and ispositioned between the impactor 2 and the spring 3. A forward section ofthis propulsion element 5 is a disk 6 that slides within the forwardbody chamber 1′ and that has a slightly smaller diameter than thediameter of the forward chamber 1′. A central section of the propulsionelement 5 is a hollow cylinder 5′ that slides within the central bodychamber 1″ and that has a slightly smaller diameter than the diameter ofthe central chamber 1″. This section 5′ extends into the front chamber1′ and is attached to the disk 6. A rear section of the propulsionelement 5 is a hollow cylinder 5″ having an inner diameter equal to thatof the central section 5′ and having outer diameter slightly less thanan inner diameter of the spring 3, so as to form a circular lip orshoulder around which the spring is seated. A perpendicular cylindricalholding rod 7 traverses the vertical center of the central section 5′and is attachable to that section. This rod 7 extends out of the centralchamber 1″ of the cannon body 1 through horizontal slits (not shown) inthe side of the chamber wall. The spring 3 is compressed when rod 7 andattached compression/propulsion element 5 are pulled backward. Theimpactor 2 has a curved convex forward-facing surface 2′ and a flatbackward-facing surface 2″ that initially rests against the slidabledisk 6 in the front chamber 1′. A concentric cylindrical knob 6′ isattached to the center of the disk 6 to help support the impactor 2 byresiding within a cylindrical indentation 2′″ at the center of the flatrear side 2″ of the impactor. Another component of the cannon is acompression/release element or assembly 8, illustrated in detail in FIG.5. This assembly 8 comprises a horizontal threaded rod 9 with a hollowforward-facing locking/release element 10 attached at the front end anda perpendicular or transversely oriented turning/constraining rod 11attached near the back end. In between these elements, and mounted tothe rod 9, is a flange nut 4 with internal threads that match those ofthe rod 9. The locking element 10 is a blind mate or bayonet mount typeof connector, in the form of a hollow cylinder provided with twodiametrically opposed L-shaped forward-facing slots 12. This element 10slides within the rear sections 5′ and 5″ of the propulsion element 5and attaches to the transverse holding rod 7 when pressed against thisrod and rotated, causing the rod to become set within an upper orrearward section of each L-slot 12. The rotation of the locking element10 is effected by rotation of the turning/constraining rod 11 whoseorientation is aligned with the locations of the L-slots 12 in thelocking element 10. When the locking element 10 is locked onto theholding rod 7, the attached threaded rod 9 extends backward through thecenter of the spring 3, through the flange nut 4, terminating outside ofthe cannon body 1. The flange nut 4 has three cylindrical sections 4′,4″, and 4′″ attached in series, each section having a central hole withthreads that accommodate the threaded rod 9. The forward section 4′ fitsinto the rear body chamber 1′″, and, having a slightly smaller outerdiameter than the diameter of this chamber, is rotatable therein. Thecentral section 4″ of the flange nut 4 has a larger diameter that actsas a stop preventing the inserted forward section 4′ from moving fartherforward into the rear chamber 1′″ of the cannon body 1. The rear section4′″ of the flange nut 4 is an element that can be used to rotate thenut. This rear section 4′″ can, for example, be hexagonal, toaccommodate a wrench, or can include a gear 13′ with cogs (notseparately designated) that mesh with a gear 13 connected to a drivenshaft 14′ of an electric motor 14.

To operate the cannon 1, the compression/release device or element 8 isinserted into the rear of the propulsion element 5 until thelocking/release cylinder 10 rests against the holding rod 7. Theturning/constraining rod 11 is then oriented such that the forward endsor mouths (not separately designated) of the L-slots 12 in thelocking/release cylinder 10 are aligned with the holding rod 7. Thecylinder 10 is then moved, forward onto the holding rod 7 and rotated byusing the turning/constraining rod 11 until the locking element 10 locksonto the holding rod 7, as described above. The turning/constraining rod11 is aligned with the slot locations in the locking element 10 suchthat the rod 11 lies in the vertical direction (or any chosen direction)after the holding rod 7 is locked into place. The verticalturning/constraining rod 11 is then constrained to slide within a guiderail 15 so that the rod 11 and the attached locking element 10 can nolonger rotate. (One vertical longitudinal side wall 15′ of the guiderail 15 has a vertical slit 112′ through which the turning/constrainingrod 11 can rotate into the rail as the locking element 10 is locked ontothe holding rod 7 and has one or more slits 112″ and 112′″ farther backin the same side wall 15′ of the guide rail 15 through which the rod 11can rotate back out of the rail.) After the compression/release deviceor element 8 has locked onto the holding rod 7 and attached propulsionelement 5, the flange nut 4 is rotated on the threaded rod 9 so that theflange nut moves forward until its front section 4′ has moved into therear chamber 1′″ of the cannon body 1 and its central section 4″ restsagainst a transverse outer surface 1 a at the rear of the cannon body 1.The flange nut 4 is then rotated in place, pulling the threaded rod 9backward and moving the propulsion element 5 locked onto it back withit. (Thrust ball or roller bearings, not shown, can be inserted betweenthe central section 4″ of the nut 4 and the adjacent rear cannon surface1 a to facilitate the rotation of the nut 4.) This motion compresses thespring 3 until the length of the spring has decreased a desired amount,at which point the vertical turning/constraining rod 11 has moved backwithin the guide rail 15 to a position in line with one of the backslits 112″ or 112′″. The turning/constraining rod 11 can then be rotatedthrough that slit 112″ or 112′″ out of the rail 15, causing the lockingelement 10 to rotate in the same direction so as to release the holdingrod 7. The concomitantly released compressed spring 3 then rapidlyexpands forward, propelling the propulsion element 5 and impactor 2forward. The forward motion of the propulsion element 5 must be stoppedafter the spring 3 returns to its rest length, at which time the element5 and the impactor 2 reach their maximum speed. There are many ways toaccomplish this. One way is to couple the rear of the spring 3 to therear of the central body chamber 1″ and to couple the front of thespring 3 to the propulsion element 5. Then the spring 3 will itselfbring the propulsion element 5 to rest. A preferred way is to attachrear-facing damping springs 16 to the outer surface of the cannon body1, in line with the holding rod 7, at positions such that the rod willimpact receptacles attached to these springs after the propulsion springhas returned to its rest length. This mechanism is illustrated in FIG.4. Once the propulsion element 5 starts to slow down due to one of theserestraining mechanisms (or an equivalent one), the impactor 2 willdepart from the adjacent disk 6 and proceed forward at a preselectedspeed.

The propulsion of impactor 2 proceeds as follows. (A) The impactor 2 isinserted into the forward body chamber 1′ so that the impactor restsagainst the sliding disk 6 attached to the front of the propulsionelement 5. The back end of the propulsion element 5 rests against theforward end of the un-compressed spring 3, and the back end of thespring 3 rests against a lip or shoulder 3′ at the interface between thecentral body chamber 1″ and the rear body chamber 1″. (B) Thecompression/release device 8 is then inserted forward into the rear ofthe cannon body 1 until the attached locking element 10 moves onto theholding rod 7. (C) The turning/constraining rod 11 is then used torotate the locking element 10 so that the same locks onto the holdingrod 7 and the turning/constraining rod 11 has rotated through theforward slit 112′ into the guide rail 15. (D) The flange nut 4 is thenrotated forward into the rear chamber 1′″ of the cannon body 1 until itscentral section 4″ rests against the back side 1 a of the chamber (oragainst adjacent bearings). (E) The flange nut 4 is then rotated further(by hand, using an attached lever, or by an electric motor attached toit by suitable gears) causing the contained threaded rod 9 and attachedlocking element 10 to move backward. This movement pulls the holding rod7 and attached propulsion element 5 backward, causing the spring 3 tocompress. (F) The rotation of the flange nut 4 and consequentcompression of the spring 3 continue until the spring is compressed tothe desired length (as determined by the chosen impactor speed). At thispoint, the vertical turning/constraining rod 11, which has movedbackward in the guide rail 15, is adjacent to one of the rear slits 112″or 112′″ in the guide rail 15. (G) The turning/constraining rod 11 isthen rotated out of the rail 15 through the adjacent slit 112″ or 112′″.This rotates the locking element 10 so that the holding rod 7 isreleased and the spring 3 expands forward, propelling the propulsionelement 5 and attached impactor 2 forward. After the expanding spring 3reaches its rest length, the speed of the attached propulsion element 5begins to decrease as described above, and the impactor 2 separates fromthe disk 6 and continues forward at the preselected speed as a freebody.

The various elements in the above preferred embodiment were described indetail, but the use of alternative elements will be apparent to peopleskilled in the art. The inventive use of a spring-loaded cannon 1 topropel a free impactor 2 towards a free target can be implemented in avariety of ways. The above embodiment is efficient and effective becauseit uses the same device to lock the spring 3 onto the propulsion element5 located between the impactor 2 and the spring 3, to compress andrelease the spring 3. This device uses the rotation and translation ofthreaded rod 9, respectively executed by turning/constraining rod 11 andflange nut 4, to perform these functions. In the translation mode, therod 9 is prevented from rotating by use of a guide rail 15 thatconstrains the perpendicular turning/constraining rod 11 attached nearthe back end of the threaded rod 9. An alternative method to transitionbetween the rotation and translation of the threaded rod 9 is toincorporate the transition operation into the flange nut 4 itself, as aratcheting mechanism. Such a ratcheting flange nut 17 is illustrated inFIG. 6. The mechanism allows the nut 17 to turn freely in one direction,to pull back the threaded rod 9 and compress the spring 3, but preventsthe nut 17 from turning in the opposite direction on the threaded rod 9.When the nut 17 is rotated in this opposite direction, it locks into alongitudinal slit 18 in the inserted threaded rod 9 and rotates theattached rod in the same direction. This rotation unlocks the propulsionelement 5 and releases the compressed spring 3. This mechanism thusenables the nut 17 to pull the rod 9 backward to compress the spring 3when the nut 17 turns in one direction and to unlock the holding rod 7and release the compressed spring 3 when the nut 17 is turned in theopposite direction. If this device is used, the guide rail 15 is notnecessary to prevent the rod 9 from rotating but can still be includedas a safety mechanism to prevent the accidental release of thecompressed spring 3.

Another option is to forgo the simplicity of using the same device 8 tolock, compress, and release the spring, and use a separate device tohold and release the spring 3 after compression thereof. Such a separatedevice is illustrated in FIGS. 7A-7C. This device consists of a seriesof gears 19 attached adjacent to each side of the cannon body 1. Theseside gears 19 are used to rotate a cylinder 20 with a slot 21 that locksonto the inserted holding rod 7 after the spring 3 is compressed. Afterthe holding rod 7 is locked into holding chamber or slot 21 of cylinder20, which is connected to the gears 19, the compression/releasemechanism 8 is unlocked from the bar 7 and removed from the cannon 1.The rod 9 and spring 3 can then be released by rotating the side gears19 in the opposite direction. The rotations of the side gears 19 can beimplemented by using an attached lever (not shown) or an attachedelectric motor 22.

In the NOCSAE-style helmet drop, illustrated in FIG. 1, the fallinghead/helnnet 1101 is guided downward and then back upward by two stiffvertical wires 1103. These wires 1103, together with the aluminumattachment frame 1102, prevent the rebounding head/helmet 1101 fromrotating and changing direction as it would in an actual field impact.The advantages if this system are its simplicity and ease of use. Thedisadvantages are the unnatural constraints and the infinite weight ofthe target 1104. The present improvement of such a system, shown in FIG.8, reduces the constraint disadvantage, while maintaining the targetweight disadvantage and the simplicity advantage. The two verticalconstraining wires 1103 are replaced with a single vertical central tube31 attached to a mounting plate 32 at an upper end. A concentricexternal tube 33 of larger diameter slides with minimal friction downthe internal central tube 31, guided by smooth elastic spacers 34attached to the central tube. A head model with an attached test helmet35 is attached to a support 36 at a bottom end of the outer or externalsecond tube 33. After the outer tube system 33 is raised to a desiredheight and allowed to fall onto a stationary solid anvil 37, the headmodel with helmet 35 can rebound in a different direction and rotateowing to a compression of the elastic spacers 34 that separate the inneror central tube 31 and the outer or external tube 33. The elasticity ofthe spacers 34 is chosen to be stiff enough to guide the falling outertube 33 downward, but soft enough to allow for a relativelyunconstrained rebound. Although this rebound is somewhat constrained bythe resistance of the elastic spacers 34 and limited by the geometry ofthe system, the system is a significant improvement of the completelyconstrained NOCSAE helmet drop system.

The concentric tubes impacting system of FIG. 8 can be fundamentallyimproved by introducing modifications illustrated in FIG. 9. In thissystem, a falling impactor 38 is used instead of the falling head/helmet35, and the anvil target 37 is replaced with an instrumented head/helmettarget 39. This is much more realistic than both the NOCSAE-style helmetdrop system of FIG. 1 with its strongly constrained impact on a fixedtarget 1104 and the improved helmet drop system of FIG. 8 with itslightly constrained impact on a fixed target in that both the impactor38 and the target 37 have finite weight. This system will also enablethe helmet/head target 37 to be instrumented with sensors that measurethe magnitudes of the forces transmitted through the helmet onto variouslocations on the head model.

In the testing system of FIG. 9, the falling tube 33 with attached loador impactor 38 slides with minimal friction down the fixed inner tube 31onto the instrumented helmet 39 being tested. As above, this implementsan approximately unconstrained impact and allows for an approximatelyunconstrained rebound immediately after the impact.

A preferred configuration of each internal force sensor unit 90 of aplurality of such units incorporated into the test helmet 39 for FIG. 9is depicted in FIGS. 10 and 11. Each individual sensor unit 90 consistsof a vertical cylindrical upper tube 91 containing a central spring 92.(The springs 92 model the elasticity of a player's body and enable thehead model 39 to react to an impact in a relatively realistic way.) Asolid cylindrical post 93, with a main shaft section 93′ slidablyinserted within the tube 91, rests on top of the spring 92. An upper endof the post 93 extends out of the tube 91 and terminates in a widercylinder or head 94 with a convex curved top 94′ that is to be placed incontact with an inner surface of helmet 39. Post 93 has a smallerdiameter shaft section 93″ that extended within spring 92 and thattogether with shaft section 93′ defines a shoulder 93′″ that restsagainst an upper end of the spring 92. A lower end of the spring 92rests against a contact pin 95 that applies or transmits the forceexerted by the compressed spring 92 onto a load cell or sensor 96 underthe pin. The load or sensor cell 96 has cords or leads 96′ that exit thetube 91 through slits 97 in a sidewall thereof. Upper tube 91 has athreaded bottom section 98 that screws into a threaded concentric lowertube 99 attached to a base platform 100. The height of the sensor unit90 is adjusted by rotating the upper tube 91 within the lower tube 99,and the position of the unit 90 is adjusted by sliding the lower tube 99in a radial slit 101 in the base 100. After the unit 90 is positionedwithin the respective slit 101, the unit is held place by a screw 102inserted from the bottom surface of the base 100 into the bottom of thelower tube 99. The screw 102 contains a flange nut 103 that is rotatedupward to lock the unit 90 in place. The complete device (FIG. 11)consists of a sufficient number of sensor units 90, each residing in aslit 101 in the base unit 100. The slits 101 are positioned in the base100 such that the device can provide for a uniform and comprehensivecoverage of the area of the helmet 39 that is being impacted.

The instrumented head model described above was specified in detail, butalternative constructions will be apparent to people skilled in the art.The basic inventive property of the sensor system of FIGS. 10 and 11 isproviding for the positioning the individual measurement units 90 atsufficiently many locations on the inner surface of the helmet 39 toprovide an extensive tabulation of the transmitted force distribution.

The helmet testing protocol thus proceeds as follows. The weight anddrop-height of the falling tube 33 and load 38 are chosen to achieve thedesired force and impact time applied onto the helmet 39. Anaccelerometer attached to the load 38 measures the force applied ontothe helmet 39 as a function of the time elapsed during the impact. Theimpacted helmet 39 transmits this force onto the heads 94 of the sensorunits 90, and particularly via the convex surfaces 94′ thereof, and thenonto the springs 92 and force sensors 96. These sensors 96 thus measurethe force transmitted through the helmet 39 onto the head model at eachlocation. This arrangement supplements the impact accelerationmeasurements with transmitted force measurements made on the head model.This is important because the totality of these transmitted forces canbe larger than the applied force at times during the impact, and becauseit makes it possible to measure the degree to which the impact force isbeneficially distributed over a user's skull by a helmet.

In a testing system illustrated in FIG. 12, an impact on a helmet 41 isimplemented by a flat-bottom load or block 42 with a central holetraversed by a lubricant-sheathed vertical tube 43. Instead of strikingthe helmet 41 directly, the load 42 strikes an upper end of a stiffspring 44 whose lower end rests within a cavity in upper portion of asuitably-shaped impacting element 45. The load 42 is dropped onto thehelmet 41 from various heights (which determine the impact speeds). Theload 42 slides down the lubricated vertical tube 43, which enables oneto accurately aim the load and control the rebound thereof off of thehelmet 41. The falling load 42 strikes the stiff spring 44 attached tothe impact element 45, which rests on the helmet 41. The impact isdesigned to model typical game impacts with regard to impact force andimpact time. A preferred embodiment with some modifications is shown inFIG. 13. The guide tube 43 is attached from above, and a rope and pulleyarrangement 46 is provided for raising the load 42 to the desiredheight. The impact element has a rounded lower surface 45′.

The impacts created by the system of FIG. 13 are substantiallyunconstrained because the impacting element 45 is not rigidly attachedto the falling load 42 but is free to rebound in any direction with anyspin that might be acquired during the impact with the helmet 41. Thefalling load 42 and spring 44 are constrained to rebound back up thevertical tube 43, but the impactor 45 is only lightly constrained duringmost of the impact duration.

In preferred embodiments, three types of force measurements are made foreach impact. An accelerometer 42′ attached to the falling weight 42measures the acceleration verses time profile of the impact. The forceexerted on the outside of each helmet 41 during the impact is measuredusing a sensor 44′ attached between the spring 44 and the impactor 45.The recorded data is used to confirm and supplement the data from theaccelerometer measurements made on the impactor 45. In the third type ofmeasurement, the actual forces transmitted through the helmet 41 onto ahead model 41′ are measured. These forces are recorded by force sensors(such as sensor units 90 with load sensors 96) placed at variouslocations on the model 41′, in order to determine the degree to whichthe helmets 41 are effective in spreading out the applied impact force.The outputs from these sensors 96 are transmitted to and recorded in acomputer 200 and converted into graphs or plots of force verses time, asdiscussed hereinafter with reference to FIGS. 22-28. It is to beunderstood that the accelerometer 42′, force sensor 44′, force sensorunits 90, and computer 200 are common to many, if not all of the testingapparatus disclosed herein.

The weight of the load 42 and the impact speed (or drop height) arechosen such that the force applied to the helmet 41 and the impactduration are of the order of those encountered in actual game impacts.With these loads and impact speeds, the degree of force reductionprovided by the elastic and damping properties of the helmet 41 can beevaluated and compared.

In order to compare the protective abilities of different helmets, it isnecessary to impact each helmet in the identical way. With the presentapparatus, this means that the impacts must arise from a load 42 of acommon weight w dropped onto the spring 44 from the same height h; i.e.,impacted at the same initial speed v. (Since the friction between theloads and pole is negligible, v and h are related by v=√(2gh), whereg=32 ft/s{circumflex over ( )}2 is the acceleration of gravity.)

The above-described embodiments of helmet testing systems are relativelysimple to construct and utilize because gravity supplies the impactoracceleration, but the created impact speeds are limited by the height ofthe testing room. (A 20 mph impact requires a falling distance of 13.5feet.) The rotating systems described hereinafter are more complex butcan achieve any relevant impact speed in a relatively small space. Asimple embodiment is illustrated in FIGS. 14A-14C. In this device, animpact is created by an impactor 51 attached to a rotating rod 52powered by an electric motor 52′. A counter weight 53 is attached to anend of the rod 52 opposite the impactor 51 to balance the appliedtorque. While the rod 52 accelerates to a desired angular speed, whichtypically requires several revolutions, a target helmet/head/torso 54 issituated out of a path 51′ of the rotating impactor 51. Once a desiredspeed is acquired by the impactor 51, the target or test object 54 isquickly inserted into the rotation path 51′ so that, at the completionof the next rotation, the motor 52′ will turn off and the impactor 51will strike the target 54. One way to implement the target insertion isto have the rotating rod 52 break a beam 55 between a source 55′ and asensor 55″ immediately after the rod 52 passes the location of thetarget 54. The signal from the sensor 55″ turns off the motor 52′ andtriggers a solenoid piston 52″ which inserts the target 54 into placebefore the revolution is completed.

In the simplest embodiment of this type of system, shown in FIG. 14, theimpactor 51 is rigidly attached to the rotating rod 52. The disadvantageof this is that the impactor 51 is constrained to impact and rebound ona circular trajectory. In an embodiment that creates a less-constrainedimpact, shown in FIG. 15A, the impactor 51 is elastically attached tothe end of the rotating rod 52 by a spring 56. The impact trajectory orimpactor path 51′ is still circular, but the elastic attachment allowsfor a rebound (FIG. 15B) that is much less constrained.

Another option, shown in FIGS. 16A-16C, is to have the target 54 inposition at a predetermined impact location from the start of the test,with the impactor 51 connected by a hinge 57 to the end of the rod 52,inclined or rotated towards the center of rod rotation, and locked inplace. This solution allows the path 51′ of the rotating rod 52 withattached impactor 51 to pass above the impact location of the target 54.After the desired speed is acquired, the impactor 51 is unlockedimmediately after the rod 52 passes by the target 52, for example, undercontrol of the above-described beam-breaking mechanism. The centripetalforce created by the rotation will then cause the impactor 51 to swingoutward about the hinge 57 and in alignment with the rod 52 at the endthereof so that the impactor 51 will impact the target 54 at thecompletion of the revolution. (The rotation speed of the rod 52 extendedby the swung-out impactor 51 will decrease when the impactor 51 swingsoutward, so the initial speed has to be correspondingly larger.) Asabove, the impact trajectory or path 51′ is still circular, but thehinged attachment allows for a rebound of the impactor 51 that is muchless constrained. An option is to have the outer end of the rotating rod52 inserted into a radial hole in the impacting element 51. The element51 is held in place during the initial rotations and is releasedimmediately after the rod 52 passes by the target 54, and specificallyabove the target in the case that the path 51′ is in a vertical plane,so that the centripetal force created by the rotation will then causethe impactor 51 to move outward into place at the end of the rod 52 andimpact the target 54 at the completion of the revolution. (The rotationspeed of the extended rod 52 will decrease when the impactor 51 slidesoutward, so the initial speed has to be correspondingly larger.)

In order to achieve a completely unconstrained impact, the impactor 51can be set free, that is released from the rod 52, at the bottom of therotation path 51′ before impact with the target 54. In a preferredembodiment of this arrangement, shown in FIGS. 17A-17C the impactor 51is held in place during the rotations by the inertial force created bythe rotation, and by a short perpendicular rod 59 attached to therotating rod and inserted into a hole 60 in the back face of theimpactor. After the desired impactor speed is acquired, the rotating rodis abruptly stopped at the bottom of the rotation path, initiated, forexample, by the above beam-breaking mechanism. The signal from thesensor 55″ triggers a solenoid piston 61′ that inserts a perpendicularstopping rod 61 into the path of the rotating rod 52 whilesimultaneously turning off the electric rotation motor 52′. This causesthe impactor 51 to separate from the rod 52 and continue forward in astraight line (tangential to the circular rotation path 51′) with thedesired velocity, until it strikes the target 54 that has been insertedupwards as described above, into the rotation path 51′ of the impactor51. In this system, the impactor 51 is completely unconstrained duringthe impact and is thus free to rebound in any direction with any spin.

In each of the above-discussed rotary test-apparatus embodiments, theimpactor 51 and target 54 can be instrumented as in the previousembodiments in order to measure the relevant performance metrics. Thiswill be described in detail hereinafter.

The detailed description above relates to embodiments of devices thatpropel a free or substantially free impactor towards a target. Nowdescription will be provided of preferred embodiments of free orsubstantially free targets that are to be struck by these impactors.These targets have three aspects: (1) a target body that consists of ahead/neck/torso model with an attached helmet, (2) a mechanism forrendering this assembly as a free or substantially free body before orat the time of an impact, and (3) incorporated sensors that record theforces applied to and through the attached helmet.

The head/neck/torso model should conform to the body of a helmet user inshape, weight distribution, and elasticity. The body-part weights areknown, but the amount of the torso that is relevant must be estimated.The relevant amount depends on how far the impact wave extends into thetorso during course of the impact. Since, for a given impactor weightand velocity, the forces applied on the target increase when the targetweight decreases, it is important to choose the total model weight atthe lower end of possibilities in order that the effect on the lightesthelmet users is taken into account. If a helmet provides an acceptablemeasure of safety for the lightest users, it will provide an acceptablemeasure of safety for the all users, whereas the converse is not true.

The incorporation of body elasticity into the target must also be anapproximation. For a human target, this elasticity can be beneficiallychanged by adjusting the tensions within the relevant body musclesduring the impact. However, the chosen strengths and distributions ofelastic elements within the target must reflect the possibility that thehelmet user will not have the time or ability to make effectiveadjustments.

There are a variety of ways to incorporate elastic elements into thetarget. The neck of the model can be approximated by a suitable springor group of springs. It is also possible to support the target withsuitably placed springs. Such springs not only model human bodyelasticity, but the also render the target to be relatively free duringthe impact. An example of this is shown in FIGS. 18 and 19. In thisembodiment, a head model 71 is attached to a vertical rod 72 that issupported in a universal joint 73 mounted to a holder or bracket 73′ byrigid arms 73″ and steadied or oriented by a plurality of attachedhorizontal springs 74. In another preferred embodiment, springs can beintegrated directly into the force sensors, as above with reference tosensor units 90.

As indicated above, it is desirable for the target to be a completelyfree body during the impact. A preferred way to accomplish this is tosupport the target from above with suitably placed strings or lightwires before the impact, and to disconnect these supports immediatelybefore the impact or at the start of the impact. An embodiment of suchan arrangement is shown in FIG. 20. A cannon 75 (see discussion abovewith reference to FIG. 4 et seq.) propels an impactor 76 towards atarget helmet 77. A head/neck/torso model 78 with the helmet 77 attachedthereto is supported by three wires 79 prior to an impact. By adjustingthe lengths of wires 79 and/or the orientation of the model 78, theimpact can be directed at any location on the helmet 77. The wires 79,initially attached to a holding/release device 80 located above themodel 78, are released immediately prior to each impact. A preferred wayto do this is to have the wires 79 held by an electromagnet 79′ that isswitched off when the impactor 76 breaks a beam 79″ that is located infront of the helmet 77. (As described above with reference to beam 55,the device may include a beam source 55′ and a sensor 55″.) Anotherpreferred method is to have the holding/release device 80 configured asa force-sensitive receptacle. An embodiment of such a device is shown inFIGS. 21A and 21B. A piston 81 that is biased or loaded by springs 81′and that supports the wires 79 is initially held in place by aball-bearing lock 82 placed within a tapered cavity 83 in the sidewall(not enumerated) of the piston. The ball lock 82 extends into anindentation 84 in the wall of a fixed or stationary cylinder 85 thatsurrounds the piston 81 and a casing 81″ thereof. The device 80 isconfigured so that the piston 81 and attached wires 79 are released whenthe (threshold) force on the springs 81′ exceeds the weight of thetarget by a small amount. If the impact causes the target to moveupwards, the wires are irrelevant and the target acts as a free body,but if the impact causes the target to move downwards or backwards, theforce exerted on the device will immediately exceed the threshold andthe target 77/78 will again become a free body. More specifically, adownward or backward impact force pulls piston 81 down, compressingsprings 81′ and freeing ball lock 82 to move out of indentation 84. Atthat point the piston assembly, including casing 81″ falls together withwires 79, model 78 and helmet 77.

The force exerted on the target 77/78 by the impactor 76 during theimpact can be measured by accelerometers placed at appropriate locationswithin the impactor 76 and the target 77/78. It is especially importantto record accelerations at the center of mass of the target 77/78 inorder to measure the total applied force, and at a head section 78′ ofthe model 78, in order to measure the acceleration of the head. (Thetotal applied force can also be measured by an accelerometer placed atthe center of mass of the impactor 76.) In addition to measurements ofsuch applied forces, it is important to measure the forces transmittedthrough a helmet 77 onto the head model 78′, as explained above withreference to FIG. 2. Preferred methods to perform these additionalmeasurements will be described below.

One preferred way to measure the magnitudes and distributions of theforces transmitted through a helmet onto the head of a user is toposition a series of force sensors between the inner surface of thehelmet and the outer surface of the head model as discussed above withreference to FIGS. 10 and 11. To accommodate the variety of availableinner helmet surfaces, the positions and heights of the sensors arepreferably adjustable (e.g., see reference designations 91, 99, 101) sothat the sensor units 90 and particularly the convex curved tops orupper surfaces 94′ thereof can come into contact with the inner helmetsurface at each of the desired locations. Also, the elasticity of thehead, neck, and torso of a helmet user can be preferably integratedwithin the structure of the sensors.

Data Analysis

The present helmet testing equipment, unlike the prior art equipment,provides free-body impacts that closely replicate actual field impacts.Now preferred methods of analyzing the data obtained from the use ofthis equipment will be described. This description entails thedefinition of performance metrics, both traditional and inventive, thateffectively characterize the measured data. These metrics can be used tocompare lab and field impacts, to determine the protective capabilitiesof helmets, and to compare and regulate available helmets.

Data obtained from impacts produced by effective helmet testingequipment can serve three functions. (1) The data can be used to comparelab and field measurements in order to determine if the lab measurementsare realistic. (2) After a positive comparison, the lab data can be usedto supplement measurements of field impacts in order to more fullycharacterize these impacts. (3) The lab data can be used to measure andcompare the protective capabilities of various helmets in order to helpusers and associations choose the most protective products.

Parts a and b below define and illustrate metrics that characterizeacceleration data. Part c defines and illustrates metrics thatcharacterize transmitted force data.

a. Accelerometer Data

Accelerometer measurements obtained from a single impact providethousands of data points and so, in order to effectively characterizethe impact, the important aspects of these data must be reduced to arelatively small number of performance metric values. The rawacceleration data consists of lists {a[i]; i=1, 2, . . . , N} ofacceleration (g) values recorded for each measurement, or, equivalently,lists {a(t); t=t1,t2, . . . , tN} of acceleration values recorded foreach measurement time. (If the measurements are made at times equallyspaced by an amount dt, then ti=i·dt.) Typical values for thesequantities are N=2500, dt=0.00001 s, so that tN=0.025 s.

The conventional metrics evaluated from these lists are the maximumrecorded acceleration ma, the average recorded acceleration aa, thetotal impact time tt, and the severity index si. For the above equallyspaced measurements,

tt = N ⋅ dt${aa} = {\frac{1}{N}{\sum\limits_{i = 1}^{N}\;{a\lbrack i\rbrack}}}$${si} = {{di} \cdot {\sum\limits_{i = 1}^{N}\;{a\lbrack i\rbrack}^{1.5}}}$

Another important, but often overlooked, metric is the coefficient ofrestitution (cor). This is the positive ratio of the relative reboundspeed v′ and the relative incident speed v of an impact:

${cor} = {\frac{v^{\prime}}{v} = {1 - {\frac{g \cdot {dt}}{v} \cdot {\sum\limits_{i = 1}^{N}\;{{a\lbrack i\rbrack}.}}}}}$

The fractional kinetic energy loss during an impact is 1-cor². Duringthe collision between a helmet and an impacting load, the helmetmaterial is compressed and decompressed, and during this oscillation thematerial absorbs and releases elastic and thermal energy. The elasticenergy is largely returned to the load and the thermal energy is largelydissipated as heat. The more of the incident load kinetic energy that isconverted into thermal energy, the smaller will be the force exerted bythe load on the helmet.

These metrics ma, aa, si, and cor are measures of the effectiveness of ahelmet in reducing the force applied on it during an impact. The helmetfor which the magnitudes of these quantities are the smallest is the onethat provides the greatest measure of safety for a helmet user.

A plot of the data obtained from a typical impact measured using aprototype of the present equipment is shown in FIG. 22. For these data,the evaluated metric values are

-   -   M={ma=40.6 g, aa=17.4 g, tt=0.025 s, si=68.5 s, and cor=0.221}.        Previous analyses of impact data have relied on one or more of        these metrics, or on related ones. However, these metrics alone        do not adequately characterize the impact because they fail to        describe important details about the acceleration data. These        details include descriptions of the shape, slopes, and local        curvatures of the data plots. Additional metrics set forth below        supply these missing details.        b. Frequency Analysis

It is proposed herein to tabulate the harmonic frequency (Fourier)spectrum of the acceleration data. The first approximation to these datais given by the Sin function asa1(t)=c1·Sin(ω1·t),where the fundamental frequency is ω1=π/tt rad/s. This function ofcourse does not provide an accurate representation of the accelerationlist {a[i]} plotted in FIG. 22, but an accurate representation of thedata is obtained by adding together the first few (n) harmonics,

${{an}(t)} = {\sum\limits_{i = 1}^{N}\;{{ci} \cdot {{Sin}\left( {\omega\;{i \cdot t}} \right)}}}$where the i'th frequency isωi=πi/tt

An excellent fit to the data plotted in FIG. 22 is provided by the suma5 of the first five harmonics (n=5). The amplitudes C5={ci} are

-   -   C5={29.48, 8.20, 5.58, −3.70, −0.52},        and the plot of a5(t) vs t is shown in FIG. 23 (in red),        superimposed with the data plot. The plots are almost identical.        Plots of the five included harmonics are shown in FIG. 24. The        list of metric values M={ma, aa, tt, si, cor} together with the        list C5 of harmonic amplitudes provide a much more informative        characterization of the impact than do the conventional metric        values alone.

Using lab equipment described herein, acceleration data can be obtainedfor any encountered impact speed, and for the range of relevanthelmet-head-neck-torso weights (Field impacts have been measured toreach relative speeds as high as 20 mph, and the weights vary from 10 to30 lbs.) An important application is to use the equipment to determinehow the various metric values depend on the various speed and weightvalues.

c. Transmitted Force Data

The acceleration data described above determine the values of themaximum and average forces applied on a target helmet during an impact.(The applied forces are the product of the applied accelerations and theweight of the impactor.) These values are, however, only a part of thedetermination of the protective capabilities of a helmet. For a givenapplied force profile, the helmet that spreads the consequent forcestransmitted through the helmet onto the skull of a user over the largestarea and largest time interval will offer the best protection. Thepreferred method to determine this force distribution is to placesuitably designed force sensors at various locations on the target skullmodel under the helmet, as discussed above with reference to FIGS. 10and 11.

If a total of N such force sensors are used, the preferred metrics thatsummarize the transmitted force values are the following. (1) Themaximum force recorded on each of the N sensors. (2) The largest ofthese N maximum forces. (3) The sum of these N maximum forces. (4) Themaximum of the sum of the N forces as a function of the impact time. Thesignificance of this information is as follows. (1) The maximum forcemeasured on a sensor under the helmet is a measure of how much of theapplied force is transmitted through the helmet onto the sensor. It is ameasure of the effectiveness of a helmet in spreading the applied forceover the body of the player. The smaller the collective values of thesetransmitted forces compared to the maximum applied force, the moreeffective is the tested helmet in spreading out the force over thesurface of the user's head. (2) In particular, it is obviously desirableto have the maximum individual transmitted force, and the sum of suchforces that act together in the same area, significantly less than aforce capable of causing a MTBI, even if the maximum applied force isabove that level. (3) The sum of the maxim force values is a simplemeasure of the distribution of the applied force. This sum is usuallyless than the maximum applied force because it is not possible to coverthe entire skull surface with sensors, but it could in principle belarger because the individual maxima can occur at different times duringthe impact. (4) The maximum of the sum of the transmitted forces (MSTF)is the best force distribution metric because it takes into account thefact that the individual force maxima can occur at different timesduring the impact. It is highly desirable for the maximum values of atleast some of the transmitted forces to occur at different times duringthe impact so that the combined effect of these forces is diminished andthe MSTF is reduced. For a given impact and given applied force profile,the helmet that reduces the magnitudes of this quantity the most is thehelmet that provides the greatest measure of safety for the footballplayer.

It is important to note that it is possible for this maximum totaltransmitted force to be greater that the maximum applied force. This isnot possible in an equilibrium situation, but at times during an impactthe transmitted force can be greater than the applied force. (We havedemonstrated that this is consistent with the laws of mechanics andthermodynamics by constructing mathematical models of the presentmeasurement system and helmet, and numerically solving the correspondingdifferential equations of motion. The solutions demonstrate the effectin question.)

To exhibit the profiles of transmitted forces, consideration is given tothe measured impact whose applied force profile is given in FIG. 25. Atotal of 5144 force measurements were made during the total impact timeof 0.05144 sec. The maximum recorded force of 217.2 lbs occurred after0.02389 sec. The measured transmitted force profiles from five preferredsensor prototypes (as described in Sec. 8.g) are given in FIG. 26A. Themaximum recorded transmitted forces are 59.2 lbs, 50.8 lbs, 50.8 lbs,46.5 lbs, and 21.2 lbs, which sum to 228.5 lbs. The profile for the sumof these forces is given in FIG. 26B (in red). (The horizontal axis hasbeen changed from sec to sec*10⁵ for comparison with FIG. 25.) Theapplied force profile of FIG. 25 has been superimposed on the totaltransmitted force plot. The total transmitted force is seen to exceedthe applied force at various times during the impact. The maximum valueof the sum of the individual transmitted forces (the total transmittedforce) is 224.2 lbs. This is slightly smaller than the sum of themaximum values of the individual transmitted forces because theindividual maximum values occur at different time during the impact, andit is slightly larger than the maximum applied force of 217.2 lbs. Thisexample illustrates the importance of measuring the transmitted forcesin addition to the applied force. Examination of the applied force alonewould undervalue the size of the maximum force applied on the helmetuser's head during the given impact.

d. Comparison of Free and Constrained Impacts

It was explained above how the constrained impacts used in the prior arthelmet testing methods are very different from the free body impactsarising in football games. The stages in a free body impact areillustrated in FIG. 2. The impacting body (left side) compresses ontothe target body as it slides forward so that the impactor is subject toan upward elastic force in the direction perpendicular to the localtarget surface and a backward sliding friction force in the directionparallel to the local target surface. The elastic force is in effectuntil the impactor rebounds off of the target, and the sliding frictionforce is in effect until either the impactor begins to execute purerolling on the target or it departs from the target. (Pure rollingoccurs when the linear speed equals the product of the rotational speedand the effective radius.) In either case, the impactor rebounds fromthe target after decompressing and after moving forward a certaindistance on the target, while acquiring a certain amount of forwardrotation. (For clarity, the sliding/rolling distance shown in thedrawing is greatly exaggerated.) If, on the other hand, the impactor isnota free body but is constrained to rebound in the same direction asthe incident direction, the impactor can neither slide on the target noracquire a rotation. In this case, the forces acting on the impactor arethe physical perpendicular elastic force and the net artificialconstraining force that prevents the sliding motion and, together withthe elastic force, directs the impactor to rebound in the incidentdirection. In other words, the constraint replaces the backward-directedphysical friction force, a force that decreases the impactor's forwardsliding speed and increases it's rotational speed, with a very differentbackward-directed artificial constraining force that completely preventsthese motions from occurring. (In the free case, angular momentum isconserved and the target acquires a compensating forward rotation. Inthe constrained case, the target also acquires a forward rotation fromthe applied torque, but the value of this rotation is in general verydifferent from the value that arises from a free impact.)

In a recorded use of the cannon of FIG. 4, the rebound direction ofimpactor 2 is clearly seen to differ from the (horizontal) incidentdirection, and the impactor is seen to acquire a (counterclockwise)rotation after impact. See FIGS. 29A and 29B. Neither of these physicaleffects can occur in the impacts used in the prior art. The reboundmotion that occurs in such constrained impacts would look exactly likethe incident motion.

The differences between free and constrained impacts are also readilydisplayed in the applied force data measured during these impacts. Dataobtained using the vertical tube device described above with referenceto FIG. 8 in which a falling helmet and head model 35 impacts onto afixed solid plate or anvil 37 are shown in FIG. 27. The device of FIG. 8replicates the impacts created in the NOCSAE equipment (FIG. 1). Thesame helmet was subjected to impacts using the prototype of thepreferred embodiment of the cannon described above with reference toFIG. 4 and target body described with reference to FIGS. 18 and 19.These free body impacts were directed at the same helmet location withthe same velocity used in the constrained falling-helmet impacts. Theresults of applied force measurements on this helmet are shown in FIG.28. For comparative purposes the two plots have been normalized so thatthe maximum forces have the same value (350 lbs). The differencesbetween the two plots are apparent. The plot of the data from theconstrained impact shows a relatively smooth curve with minimalstructure, whereas the plot of the data from the free body impact showsconsiderable structure in the form of higher frequency oscillationssuperimposed on the primary curve. These oscillations are real, arisingfrom the weakly-damped elasticity of the padding used in the impactedhelmet, and would occur in a game impact at the given velocity and givenlocation on the helmet, but they have been almost completely suppressedby the artificial forces created in the constrained impact.

It is clear from the above theoretical and experimental demonstrationsthat important differences exist between the unconstrained impactstaught herein and the constrained impacts used in the prior art.Depending on the values of the sliding friction coefficient and CORbetween an impactor and a helmet, the maximum acceleration recorded in aconstrained impact can be significantly less then that which obtains ina real impact between the same impactor and helmet at the same locationand velocity. This means in particular that the helmet testing andcertifications provided by the use of constrained impacts are noteffective in furnishing accurate information about the degree ofprotection provided by football helmets.

What is claimed is:
 1. A method for testing a helmet for effectivenessof user protection, comprising: moving a load along a predeterminedpath; supporting a target body at an impact location in saidpredetermined path, said target body including a head model and a helmetdisposed on said head model; impacting said target body with a forcegenerated by the moving of said load, the impacting of said target bodyincluding contacting said target body with an impactor free to moveperpendicularly and tangentially relative to a surface of said targetbody; at least partially reducing the supporting of said target bodybefore or during the impact of said impactor with said target body atsaid location; and automatically measuring forces generated during theimpact of said impactor with said target body at said location.
 2. Themethod defined in claim 1 wherein said load includes said impactor, themoving of said load including restraining said impactor during aninitial portion of said predetermined path and further including atleast partially eliminating the restraining of said impactor at or priorto impact of said impactor with said target body at said location. 3.The method defined in claim 2 wherein the moving of said impactorcomprises dropping an impactor support member from a predeterminedheight, said impactor being attached to said support member.
 4. Themethod defined in claim 3 wherein said support member is a tube, saidimpactor being attached to a lower end of said tube, said tube being anouter tube slidably disposed coaxially about a fixed or stationary innertubular member of a smaller diameter than a diameter of said tube, saidlocation being below said tube and said fixed or stationary innertubular member.
 5. The method defined in claim 2 wherein said impactoris a contact element resting on the helmet of said target body andwherein the moving of said load comprises sliding dropping said loaddown along a fixed vertical rod onto a spring inserted into said contactelement.
 6. The method defined in claim 5, further comprising operatinga series of pulleys to raise said impactor to said predetermined height.7. The method defined in claim 2 wherein said impactor is connected to arotatably supported rod, the moving of said load comprising rotatingsaid rotatably supported rod at an accelerating angular speed, furthercomprising inserting said target body into said predetermined path atsaid impact location after and only after a desired impactor speed isattained.
 8. The method defined in claim 7 wherein said impactor ispivotably mounted via a hinge to an end of said rotatably supported rod,further comprising: releasably retaining said impactor at a positionalong said rotatably supported rod inward of said target location duringrotating of said rotatably supported rod at the accelerating angularspeed; and once the desired impactor speed is attained, releasing saidimpactor to rotate about a pivot axis of the hinge so that said impactorrotates outward to strike the target body at said impact location. 9.The method defined in claim 7 wherein said impactor is releasablymounted to an end of said rotatably supported rod, further comprising:arresting motion of said rotatably supported rod; and propelling saidimpactor from said rotatably supported rod proximate said impactlocation, after the desired impactor speed is attained.
 10. The methoddefined in claim 7 wherein said impactor is mounted to an end of saidrotatably supported rod via a spring coupling, whereby multiple degreesof freedom are provided to motion of said impactor upon impacting saidtarget body.
 11. The method defined in claim 2 wherein the moving ofsaid impactor comprises operating a cannon device to propel saidimpactor.
 12. The method defined in claim 11 wherein the operating ofsaid cannon device includes compressing a spring, holding the compressedspring in place, and releasing the compressed spring to propel saidimpactor.
 13. The method defined in claim 1 wherein the supporting ofsaid target body at said impact location includes suspending said targetbody by elongate tensile members attached to an element configured torelease the elongate tensile members; and operating said element torelease said target body prior to the impact of said impactor with saidtarget body or in response to engagement of said impactor with saidtarget body.
 14. The method defined in claim 13 wherein said elementincludes an electromagnet, the operating of said element includingswitching off said electromagnet immediately before the impactor strikesthe target body.
 15. The method defined in claim 13 wherein said elementis a force-sensitive receptacle that releases the strings when the forceon the strings exceeds the weight of the target by a small amount. 16.The method defined in claim 1 wherein the automatic measuring of forcesincludes operating a plurality of force sensors spaced from one anotheron said head model.
 17. The method defined in claim 16 wherein saidforce sensors are disposed between an inner surface of said helmet andan outer surface of said head model.
 18. The method defined in claim 1,further comprising operating a computer or processor to determine impactacceleration data including one or more of the following: maximumrecorded acceleration, average recorded acceleration, total impact time,severity index, and coefficient of restitution.
 19. The method definedin claim 1 wherein the automatic measuring of forces includes operatingan accelerometer attached to said impactor.
 20. The method defined inclaim 1 wherein the supporting of said target body at said impactlocation includes supporting said head model on a rod attached to aholder or bracket via a plurality of springs each extending at leastpartially transversely or perpendicularly to said rod.